Glacial Lake Evolution (1962–2018) and Outburst Susceptibility of Gurudongmar Lake Complex in the Tista Basin, Sikkim Himalaya (India)

Round 1

Reviewer 1 Report

Glacial Lake Evolution (1962-2018) and Outburst Susceptibility of Gurudongmar Lake Complex in the Tista basin, Sikkim Himalaya (India)

The manuscript presents a very interesting case study of a paternoster lake complex in northern Sikkim: the Gurudongmar Lake Complex. This original study is based on multitemporal satellite data (Corona, Hexagon, Landsat, Sentinel) and field inspections. In all sections the manuscript is written in a very clear, well-structured, and straight forward style that attracts a broader audience. The evolution of the different lakes is very detailed and interesting. The introduction provides a clear statement of the research problem and a good overview of relevant literature, both on a global scale and specific for the site-specific regional scale of the Eastern Himalaya and Sikkim. When the authors refer to “long time triggers” like dead ice melting “ (line 49), it might be useful to consider the study by Schmidt et al. 2020 on a GLOF event in the Trans-Himalaya of Ladakh. In this case thawing of dead ice in the moraine was the trigger for subsequent tunneling (Schmidt et al. 2020. Cryosphere hazards in Ladakh: the 2014 Gya glacial lake outburst flood and its implications for risk assessment. Natural Hazards 104, 2071–2095. doi:10.1007/s11069-020-04262-8). As ice-cored moraines are in GL 2 and GL 3 (Table 6, bottom) this mechanism could also be relevant for potential GLOFs in this case study in upper Sikkim.

The section on the study area contains a lot of useful and very detailed information and is presented in a straight forward style. Maybe, but not necessariy, the part on the geology (lines 121-133 can be reduced. The maps in Fig. 1 are useful and interesting. The method section is also written in a concise way and contains all important aspects (different formulae by Huggel et al., Liu et al., Sharma et al.; three different methodologies by Wang et al., Emmer and Vilimek, Rounce et al. in Table 3). The results are also presented in a detailed and very clear style. It is a very useful susceptibility assessment overview for the region of Sikkim. The discussion provides a broader regional context including eastern Nepal and Bhutan. In the last part of section 5.2. (dead ice in a damming moraine) the mentioned paper by Schmidt et al. might be useful. 

To conclude, this is a very useful and well researched paper!

Some minor comments:

Sometimes “glacier retreat“, in other cases “glacial retreat” (line 41). This should be coherent throughout the text.

Line 41 delete “the” before glacier retreat

The different scenarios (page 8 top) are formatted as a table but they do not have a table caption.

A reference to Fig. 5a is made one line before Fig. 4 (line 320-321).

The last sentence of 4.3 (line 348) “The probability … is described in the next section.” Is not necessary.

Line 577 Study (typo)

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Much attention is paid on the changing investigation and hazards assessment of glacial lakes in the process of recent climate change. This is a comprehensive depiction on an interesting topic of assessment the glacial lake long evolution (1962-2018) and outburst susceptibility on the four investigated glacial lakes in Tista basin, Sikkim Himalaya (India). The writing is easy to understand. However, I think the manuscript should be rewritten with essential improving at this version and some major corrections at least included:

• Overall, I think the discussion should be essentially strengthened in manuscript. I strongly suggested that the authors comprehensively inspected the relative documents and provide further analysis, explanation, comparison on the differences of evolution and hazards of surveyed glacial lakes, especially based on field inspections and measurements data.
• What data were obtained during the field inspections and measurements process?
• More detailed information about the uncertainties is suggested to be provided (in e.g., in lake area and volume).
• The highly GLOFs hazard-prone driven parameters (such as slope movement into the lake, calving, earthquake, and melting of buried ice) should be further discussed with more detailed facts, since the field inspections and measurements have been conducted during the period 2017–2018.
• In Table 2, there exists a problem of “area is always contained in volume”. Better use the relation between lake depth and lake area as given in the same work: as area is always contained in volume, estimating volume from area primarily means to estimate area from itself – this works and is quite popular but simple nonsense (See: Cook SJ et al. 2015. Estimating the volume of Alpine glacial lakes. Earth Surface Dynamics; Wang X, et al. 2012. An approach for estimating the breach probabilities of moraine-dammed lakes in the Chinese Himalayas using remote-sensing data. Natural Hazards and Earth System Sciences).
• Some sentences and contents should be reorganized. e.g., In line 68-72, the documents should be summarized and commented not just listing references itself; it seems that the contents in line 72-77 belong to description of “study area”.
• In the section of “Future possible evolution of GLC”, further discussion/ methodology are asked to support the area data of GL-2, GL-3, and GL-4 in 2028.

Author Response

Please see the attachment.

Author Response File: Author Response.docx